Method and apparatus for performing component carrier-specific reconfiguration

ABSTRACT

Methods and apparatus are described. A long term evolution (LTE) base station includes a transmitter and a processor. The processor coordinates with another LTE base station and, based on the coordination, determine subframes during which the LTE base station is to reduce transmission power so that the other base station can transmit on a same carrier frequency in the determined subframes. The transmitter and the processor send configuration information to a wireless transmit/receive unit (WTRU). The configuration information includes a medium access control (MAC) based discontinuous reception (DRX) configuration and an indication of subframes during which the base station is to reduce transmission power. The transmitter and the processor transmit data to the WTRU in subframes based on the determined subframes and the MAC based DRX configuration of the WTRU.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/174,302, filed Jun. 6, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/497,481, filed Sep. 26, 2014, which is acontinuation of U.S. patent application Ser. No. 12/722,872, filed Mar.12, 2010, which issued as U.S. Pat. No. 8,873,505 on Oct. 28, 2014,which claims the benefit of U.S. Provisional Application No. 61/159,606filed Mar. 12, 2009, the contents of which are hereby incorporated byreference herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

In order to support higher data rate and spectrum efficiency, newwireless technologies have been introduced. For example, the thirdgeneration partnership project (3GPP) long term evolution (LTE) systemhas been introduced into 3GPP Release 8 (R8).

The LTE downlink (DL) transmission is based on orthogonal frequencydivision multiple access (OFDMA) air interface, and the LTE uplink (UL)transmission is based on single-carrier (SC) DFT-spread OFDMA(DFT-S-OFDMA). The use of single-carrier transmission in the UL ismotivated by the lower peak-to-average power ratio (PAPR) compared tomulti-carrier transmission such as orthogonal frequency divisionmultiplex (OFDM). For flexible deployment, the 3GPP R8 LTE systemssupport scalable transmission bandwidths of either 1.4, 2.5, 5, 10, 15or 20 MHz. The R8 LTE system may operate in either frequency divisionduplex (FDD), time division duplex (TDD) or half-duplex FDD modes.

In the R8 LTE system, each radio frame (10 ms) consists of 10 equallysized sub-frames of 1 ms. Each sub-frame consists of 2 equally sizedtimeslots of 0.5 ms each. There may be either 7 or 6 OFDM symbols pertimeslot. 7 symbols per timeslot are used with a normal cyclic prefix,and 6 symbols per timeslot are used with an extended cyclic prefix. Thesub-carrier spacing for the R8 LTE system is 15 kHz. An alternativereduced sub-carrier spacing mode using 7.5 kHz is also possible. Aresource element (RE) corresponds to one (1) sub-carrier during one (1)OFDM symbol interval. 12 consecutive sub-carriers during a 0.5 mstimeslot constitute one (1) resource block (RB). Therefore, with 7symbols per timeslot, each RB consists of 12×7=84 REs. A DL carrier maycomprise scalable number of RBs, ranging from a minimum of 6 RBs up to amaximum of 110 RBs. This corresponds to an overall scalable transmissionbandwidth of roughly 1 MHz up to 20 MHz. Normally, a set of commontransmission bandwidths is specified, (e.g., 1.4, 3, 5, 10, or 20 MHz).The basic time-domain unit for dynamic scheduling in LTE is onesub-frame consisting of two consecutive timeslots. Certain sub-carrierson some OFDM symbols are allocated to carry pilot signals in thetime-frequency grid.

In the R8 LTE DL direction, a wireless transmit/receive unit (WTRU) maybe allocated by the evolved Node-B (eNB) to receive its data anywhereacross the whole LTE transmission bandwidth. In the R8 LTE UL direction,a WTRU may transmit on a limited, yet contiguous set of assignedsub-carriers in an FDMA arrangement. This is called single carrier (SC)FDMA. For example, if the overall OFDM signal or system bandwidth in theUL is composed of sub-carriers numbered 1 to 100, a first WTRU may beassigned to transmit its own signal on sub-carriers 1-12, a second WTRUmay transmit on sub-carriers 13-24, and so on. An eNB would receive thecomposite UL signals across the entire transmission bandwidth normallyfrom a plurality of WTRUs at the same time, but each WTRU would transmitin a subset of the available transmission bandwidth. Frequency hoppingmay be applied in UL transmissions by a WTRU.

In order to further improve achievable throughput and coverage ofLTE-based radio access systems, and in order to meet the IMT-Advancedrequirements of 1 Gbps and 500 Mbps in the DL and UL directions,respectively, LTE-Advanced (LTE-A) is currently under study in 3GPPstandardization body. One major improvement proposed for LTE-A is thecarrier aggregation and support of flexible bandwidth arrangement. Itwould allow DL and UL transmission bandwidths to exceed 20 MHz in R8LTE, (e.g., 40 MHz), and allow for more flexible usage of the availablepaired carriers. For example, whereas R8 LTE is limited to operate insymmetrical and paired FDD mode, (e.g., DL and UL are both 10 MHz or 20MHz transmission bandwidth each), LTE-A would be able to operate inasymmetric configurations, for example DL 10 MHz paired with UL 5 MHz.In addition, composite aggregate transmission bandwidths may be possiblewith LTE-A, (e.g., DL a first 20 MHz component carrier+a second 10 MHzcomponent carrier paired with an UL 20 MHz component carrier). Thecomposite aggregate transmission bandwidths may not necessarily becontiguous in frequency domain. Alternatively, operation in contiguousaggregate transmission bandwidths may also be possible, (e.g., a firstDL component carrier (CC) of 15 MHz is aggregated with another 15 MHz DLcomponent carrier and paired with a UL component carrier of 20 MHz).

FIG. 1A shows discontinuous spectrum aggregation and FIGS. 1B and 1Cshow continuous spectrum aggregation. The LTE R8 UL transmission formatuses DFT-S OFDM using a DFT precoder. The DFT precoder may be applied tothe aggregate bandwidth, (i.e., across all the component carriers), incase the bandwidths are contiguous, as shown in FIG. 1B. Alternatively,the DFT precoder may be applied per component carrier, (e.g., up to 110RBs or 20 MHz maximum), as shown in FIG. 1C.

FIGS. 2A and 2B show an intra-mobility management entity (MME)/servinggateway handover procedure in LTE R8. In LTE R8, hard handover is usedand handover procedure is restricted to one carrier, (i.e., onecomponent carrier).

An eNB is provided with a WTRU context including information regardingroaming restrictions either at connection establishment or at the lasttracking area (TA) update (step 102). The source eNB configures the WTRUmeasurement procedures according to the area restriction information(step 104). Measurements provided by the source eNB may assist thefunction controlling the WTRU's connection mobility.

The WTRU gets uplink allocation for transmission of a measurementreport, which is triggered by the rules set by, for example, systeminformation, specification, etc. (step 106), and transmits a measurementreport to the source eNB once triggered (step 108).

The source eNB makes a handover decision based on the measurement reportand radio resource management (RRM) information (step 110). The sourceeNB issues a handover request message to the target eNB at step 112passing the necessary information to prepare the handover at the targeteNB including WTRU X2 signaling context reference at the source eNB,WTRU S1 EPC signaling context reference, target cell identity (ID),K_(eNB), RRC context including the cell radio network temporary identity(C-RNTI) of the WTRU in the source eNB, access stratum(AS)-configuration, EUTRAN radio access bearer (E-RAB) context andphysical layer ID of the source cell+medium access control (MAC) forpossible radio link failure (RLF) recovery), or the like. The WTRUX2/WTRU S1 signaling references enable the target eNB to address thesource eNB and the evolved packet core (EPC). The E-RAB context includesnecessary radio network layer (RNL) and transport network layer (TNL)addressing information, and quality of service (QoS) profiles of theE-RABs.

The target eNB may perform the admission control dependent on thereceived E-RAB QoS information to increase the likelihood of asuccessful handover, if the resources may be granted by target eNB (step114). The target eNB configures the required resources according to thereceived E-RAB QoS information and reserves a C-RNTI and optionally arandom access channel (RACH) preamble. The AS-configuration to be usedin the target cell may either be specified independently (i.e., an“establishment”) or as a delta compared to the AS-configuration used inthe source cell (i.e., a “reconfiguration”).

The target eNB prepares handover with layer 1 and layer 2 and sends ahandover request acknowledgement to the source eNB (step 116). Thehandover request acknowledgement message includes a transparentcontainer to be sent to the WTRU as an RRC message to perform thehandover. The container includes a new C-RNTI, and target eNB securityalgorithm identifiers for the selected security algorithms. Thecontainer may optionally include a dedicated RACH preamble, and someother parameters, for example access parameters, system informationblocks (SIBs), etc. The handover request acknowledgement message mayalso include RNL/TNL information for the forwarding tunnels, ifnecessary. As soon as the source eNB receives the handover requestacknowledgment message, or as soon as the transmission of the handovercommand is initiated in the downlink, data forwarding may be initiated.

The source eNB generates an RRC message, (i.e.,RRCConnectionReconfiguration message including themobilityControlInformation towards the WTRU), and sends the RRC messageto the WTRU (step 118). The WTRU receives theRRCConnectionReconfiguration message with the necessary parameters(i.e., new C-RNTI, target eNB security algorithm identifiers, andoptionally dedicated RACH preamble, target eNB SIBS, etc.) and detachesfrom the source cell and synchronizes to the target cell (step 120).

The source eNB delivers buffered and in-transit packets to the targeteNB (step 122), and sends the SN STATUS TRANSFER message to the targeteNB to convey the uplink packet data convergence protocol (PDCP)sequence number (SN) receiver status and the downlink PDCP SNtransmitter status of E-RABs for which PDCP status preservation applies(i.e., for radio link control (RLC) acknowledged mode (AM)) (step 124).The uplink PDCP SN receiver status includes at least the PDCP SN of thefirst missing UL service data unit (SDU) and may include a bit map ofthe receive status of the out of sequence UL SDUs that the WTRU needs toretransmit in the target cell, if there are any such SDUs. The downlinkPDCP SN transmitter status indicates the next PDCP SN that the targeteNB may assign to new SDUs, not having a PDCP SN yet. The source eNB mayomit sending this message if none of the E-RABs of the WTRU may betreated with PDCP status preservation.

After receiving the RRCConnectionReconfiguration message including themobilityControlInformation, the WTRU performs synchronization to thetarget eNB and accesses the target cell via RACH following acontention-free procedure if a dedicated RACH preamble was allocated inthe handover command or following a contention-based procedure if nodedicated preamble was allocated (step 126).

The target eNB responds with UL allocation and timing advance (step128). When the WTRU has successfully accessed the target cell, the WTRUsends the RRCConnectionReconfigurationComplete message (C-RNTI) toconfirm the handover along with an uplink buffer status report to thetarget eNB to indicate that the handover procedure is completed for theWTRU (step 130). The target eNB verifies the C-RNTI sent in the handoverconfirm message. The target eNB can now begin sending data to the WTRU.

The target eNB sends a path switch message to the MME to inform that theWTRU has changed a cell (step 132). The MME sends a user plane updaterequest message to the serving gateway (step 134). The serving gatewayswitches the downlink data path to the target side, and sends one ormore “end marker” packets on the old path to the source eNB and then mayrelease any U-plane/TNL resources towards the source eNB (step 136).

The serving gateway sends a user plane update response message to theMME (step 138). The MME confirms the path switch message with the pathswitch acknowledgment message (step 140). By sending the WTRU contextrelease message, the target eNB informs success of handover to thesource eNB and triggers the release of resources (step 142). Uponreception of the WTRU context release message, the source eNB mayrelease radio and C-plane related resources associated to the WTRUcontext (step 144). Data packet is then transmitted via the target eNB.

In the above conventional LTE R8 handover procedure, the measurementscurrently defined to support LTE Rel-8 handover are not sufficient tosupport handover of an aggregation of component carriers in LTE-A sincea single carrier is implicitly assumed in Rel8. In addition, handover ofan entire carrier aggregation would be problematic. For example, therelative quality of each component carrier may not necessarily be thesame from each cell and so the best handover time for each componentcarrier would not be simultaneous.

SUMMARY

Embodiments for component carrier-specific reconfiguration aredisclosed. A WTRU may perform component carrier reconfiguration on acomponent carrier basis to add, remove or replace a componentcarrier(s). Discontinuous reception (DRX) and/or discontinuoustransmission (DTX) may be performed on at least one component carrier,wherein DRX and/or DTX patterns on the component carriers may notoverlap each other. A random access procedure may be performed at thetarget cell on one component carrier while other component carriers areinactive. The component carrier-specific reconfiguration or handover ofa component carrier or a channel may be implemented in coordinatedmultiple point transmission (CoMP), wherein a handover of a controlchannel, not a traffic channel, may be performed. Alternatively, ahandover of a traffic channel may be performed.

Embodiments for RRC connection signaling are also disclosed to supportthe component carrier-specific reconfiguration for the WTRU that may becommunicating with different eNBs at the same time.

Embodiments for acquiring master information block (MIB) and systeminformation block (SIB) for component carrier-specific reconfigurationoperation are also disclosed.

Embodiments for measurements to support the component carrier-specificreconfiguration and random access procedure in componentcarrier-specific reconfiguration are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A shows discontinuous spectrum aggregation;

FIGS. 1B and 1C show continuous spectrum aggregation;

FIGS. 2A and 2B show an intra-mobility management entity (MME)/servinggateway handover procedure in LTE;

FIG. 3 shows an LTE wireless communication system/access network thatincludes an Evolved-Universal Terrestrial Radio Access Network(E-UTRAN);

FIG. 4 is an example block diagram of an LTE wireless communicationsystem including the WTRU, the eNB, and the MME/S-GW;

FIG. 5 illustrates the different cell patterns for different componentcarriers of two cells;

FIGS. 6A and 6B show an example component carrier-specific handover inaccordance with one embodiment;

FIGS. 7A and 7B show another example component carrier-specific handoverin accordance with another embodiment;

FIG. 8 shows an example per-component carrier-DTX/DRX operation inaccordance with one embodiment;

FIG. 9 shows another example per-component carrier-DTX/DRX operation inaccordance with another embodiment;

FIGS. 10A and 10B show an example component carrier-specific handoverwhen CoMP is implemented in accordance with one embodiment;

FIGS. 11A and 11B show an example component carrier-specific handoverwhen CoMP is implemented in accordance with another embodiment; and

FIG. 12 is a flow diagram of an example process of RACH procedure inaccordance with one embodiment.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a computer, a machine-to-machine (M2M) device, asensor, or any other type of device capable of operating in a wirelessenvironment. When referred to hereafter, the terminology “eNB” includesbut is not limited to a Node-B, a base station, a site controller, anaccess point (AP), or any other type of interfacing device capable ofoperating in a wireless environment.

When referred to hereafter, the terminology “cell” is used to indicatethe site (including “sector”) which one or more component carriers maybe transmitted to and/or received from and may be uniquely identified,for example, by having a distinguishable pilot signal.

Adding, removing, or replacing a component carrier may or may not changethe cell that the WTRU is connected to. A WTRU may receive, (ortransmit), via multiple component carriers, and the component carriersmay or may not be from, (or directed to), the same cell. When the WTRUis configured with a group of component carriers, the WTRU may beconnected to a single cell, or may be connected to more than one cell.The WTRU may determine the cell it is connected to from one of theconfigured component carriers, (e.g., the anchor or primary componentcarrier). From the WTRU perspective, a cell may be considered anindividual component carrier or a group of component carriers.

The WTRU may receive multiple component carriers from either the sameeNode-B or different eNode-Bs and in either case the component carriersare considered as different component carriers having differentidentities even though the physical frequency bands are the same.

When referred to hereafter, the terminology “component carrierreconfiguration” includes adding a new component carrier, removing acurrently configured component carrier, and/or replacing a currentlyconfigured component carrier with a new component carrier, and mayinclude “handover” from one cell to another (removing one componentcarrier in a source cell and adding a new component carrier in a targetcell in either the same or different frequency bands). The newly addedcomponent carrier (including the newly switched component carrier) maybe on either the same eNB or different eNBs and after the componentcarrier reconfiguration the WTRU may establish links to the same ordifferent eNBs.

Even though the embodiments are disclosed with reference to controlchannels and data channels associated to 3GPP LTE or LTE-A, it should benoted that the embodiments are not limited to 3GPP LTE or LTE-A, butapplicable to any wireless communication technologies that are currentlyexisting or will be developed in the future including, but not limitedto, 3GPP high speed packet access (HSPA), cdma2000, IEEE 802.xx, etc. Itshould also be noted that the embodiments described herein may beapplicable in any order or combinations.

FIG. 3 shows an LTE wireless communication system/access network 200that includes an Evolved-Universal Terrestrial Radio Access Network(E-UTRAN) 205. The E-UTRAN 205 includes several eNBs 220. The WTRU 210is in communication with an eNB 220. The eNBs 220 interface with eachother using an X2 interface. Each of the eNBs 220 interface with aMobility Management Entity (MME)/Serving GateWay (S-GW) 230 through anS1 interface. Although a single WTRU 210 and three eNBs 220 are shown inFIG. 2, it should be apparent that any combination of wireless and wireddevices may be included in the wireless communication system accessnetwork 200 including relays with no wired connections and networkdevices that do not have the interfaces depicted in FIG. 3, (e.g., ahome eNode-B (HeNB) that has no X2 interface.

FIG. 4 is an example block diagram of an LTE wireless communicationsystem 300 including the WTRU 210, the eNB 220, and the MME/S-GW 230. Asshown in FIG. 3, the WTRU 210, the eNB 220 and the MME/S-GW 230 areconfigured to perform a component carrier-specific reconfiguration inaccordance with any embodiment disclosed herein. In addition to thecomponents that may be found in a typical WTRU, the WTRU 210 includes aprocessor 316 with an optional linked memory 322, at least onetransceiver 314, an optional battery 320, and an antenna 318. Theprocessor 316 is configured to perform a component carrier-specificreconfiguration in accordance with any embodiment disclosed herein. Thetransceiver 314 is in communication with the processor 316 and theantenna 318 to facilitate the transmission and reception of wirelesscommunications. In case a battery 320 is used in the WTRU 210, it powersthe transceiver 314 and the processor 316.

In addition to the components that may be found in a typical eNB, theeNB 220 includes a processor 317 with an optional linked memory 315,transceivers 319, and antennas 321. The processor 317 is configured toperform and support a component carrier-specific reconfiguration inaccordance with any embodiment disclosed herein. The transceivers 319are in communication with the processor 317 and antennas 321 tofacilitate the transmission and reception of wireless communications.The eNB 220 is connected to the Mobility Management Entity/ServingGateWay (MME/S-GW) 230 which includes a processor 333 with an optionallinked memory 334.

In accordance with one embodiment, a WTRU may perform componentcarrier-specific reconfiguration (i.e., adding, removing, or replacing acomponent carrier on a component carrier basis), such that a componentcarrier is added, removed, or replaced separately and independently. Thetransmit power of different carriers may be made to be different fromcomponent carrier to component carrier and from cell to cell. In thatsituation, a different ‘cell’ pattern, (i.e., “cell-edge” pattern), maybe established for each component carrier frequency. FIG. 5 illustratesapproximately the different component carrier boundaries. In FIG. 5,component carrier 1A is transmitted with a greater power than componentcarrier 2A from entity A and component carrier 2B if transmitted with agreater power than component carrier 1B from entity B that arecontrolled by the same or different eNB(s). Different per-componentcarrier cell edge boundaries may be defined for component carriers 1A,2A, 1B, and 2B, respectively. In that case, the WTRU may not be at theboundary of component carrier 1A and component carrier 2A simultaneouslyand therefore may not experience overall cell-edge conditions at anylocation on the line shown.

At P1, the WTRU may be connected to component carriers 1A and 2A. Whenthe WTRU moves from P1 to P2, the WTRU is out of component carrier 2Aboundary and enters into the component carrier 2B boundary. In thissituation, the WTRU may have better overall achievable data rates if theWTRU is receiving data via component carrier 1A and component carrier2B. A mechanism used to change a subset of component carrier(s) whilemaintaining a connection for at least one component carrier as shown inFIG. 5 is referred to component carrier-specific reconfiguration (orcomponent carrier-specific handover). Instead of switching componentcarriers, a new component carrier may be added, or a currentlyconfigured component carrier may be removed or replaced with anothercomponent carrier.

FIGS. 6A and 6B show an example component carrier-specificreconfiguration in accordance with one embodiment. FIG. 6A shows beforecomponent carrier reconfiguration and FIG. 6B shows after componentcarrier reconfiguration. In FIG. 6A, WTRU 602 receives transmission fromentity 604 on component carriers 1 and 2A. Entities 604 and 606 may becontrolled by the same eNB or different eNBs. As the component carrierreconfiguration trigger occurs for component carrier 2A, (e.g., signalquality of component carrier 2B from entity 606 becomes better thansignal quality of component carrier 2A from entity 604 by a configuredthreshold), WTRU 602 performs a component carrier reconfiguration, whichmay or may not comprise a handover procedure, as shown in FIG. 6B. Afterthe component carrier-specific reconfiguration, WTRU 602 receivestransmissions via component carrier 1 and component carrier 2B from twoentities 604, 606. It should be noted that FIGS. 6A and 6B show downlinkcomponent carriers as an example, and the reconfigured component carriermay be a DL component carrier, an UL component carrier, or both. WhileFIGS. 6A and 6B show two DL component carriers, it should be noted thatthe embodiment may be applied to any number of component carriers.

The component carrier-specific reconfiguration may be performed foruplink and downlink independently. FIGS. 7A and 7B show another examplecomponent carrier-specific reconfiguration, which may or may notcomprise a handover procedure in accordance with another embodiment.FIG. 7A shows before component carrier reconfiguration and FIG. 7B showsafter component carrier reconfiguration. In FIG. 7A, WTRU 702 receivesfrom entity 704 on DL component carrier 1 and UL component carrier 2A.Entities 704 and 706 may be controlled by the same eNB or differenteNBs. As a trigger occurs for UL component carrier 2A, WTRU 702 performsa component carrier reconfiguration such that UL component carrier 2A isremoved and UL component carrier 2B is added, as shown in FIG. 7B. ULcomponent carrier 1 remains the same since a trigger for UL componentcarrier 1 has not occurred. After the component carrier-specificreconfiguration (or handover), WTRU 702 receives on DL component carrier1 and transmits over UL component carrier 2B.

The component carrier-specific reconfiguration may be performed within acell, (i.e., adding, removing, or replacing a component carrier within acell). In this case, the component carrier reconfiguration procedure isperformed to change the set of UL and/or DL component carriers in acell. This procedure may be used to swap either a UL component carrier(or a set of UL component carriers), and/or a DL component carrier (or aset of DL component carriers). This may be performed as a DL handover orUL handover where just the physical UL channel(s) or physical DLchannel(s), (e.g., physical uplink shared channel (PUSCH)/physicaluplink control channel (PUCCH) or physical downlink shared channel(PDSCH)/physical downlink control channel (PDCCH)), may be reassigned toa new component carrier within the same cell.

When a WTRU is located at the boundary between cells (including sectors)controlled by the same eNB, the best cell according to signal strengthand/or channel quality criteria may vary dynamically. If the cells areassigned different pairs of UL/DL carriers, and if the WTRU transmits aPUCCH and a PUSCH separately on each component carrier, the eNB may makeoptimized UL/DL scheduling decisions for the WTRU based on the channelstatus reports and sounding reference signals (SRS) received via bothcells (or sectors), regardless of whether the PDCCH is received from asingle component carrier or single cell (or sector), or separately fromeach component carrier or cell (or sector).

In accordance with one embodiment, non-overlapping discontinuoustransmission (DTX) and/or non-overlapping discontinuous reception (DRX)patterns may be defined for each of the component carriers. This schememay minimize the peak-to-average ratio of UL transmissions caused by thesimultaneous PUCCH or PUSCH transmissions on the UL carriers. While thiswould have the effect of limiting the peak data rates, the WTRU and theeNB may still benefit with this scheme by selecting the best componentcarrier(s) within a given time frame especially (but not limited to) incase where the pairs of UL/DL carriers are controlled by the same eNB.For example, when an eNB knows that in given time frames certaincomponents carriers are transmitted at higher or lower powers atdifferent sites (thus making the component carrier boundaries differentin different time frames) the WTRU may be appropriately scheduled forDTX/DRX based on component carrier-boundaries in each such time frame.The non-overlapping DTX/DRX patterns may also be beneficial even if thepairs of UL/DL carriers are operated in the same cell (or sector), asthe channel quality generally varies dynamically and is differentbetween the pairs of carriers. This mode of operation may be activatedthrough an RRC message, (e.g., a handover command or otherreconfiguration command).

The per-component carrier-DTX/DRX operation disclosed above is separatefrom the DTX/DRX operation defined in a medium access control (MAC)layer in LTE. With the DRX operation in accordance with the aboveembodiment, the WTRU may not be able to receive a downlink channel,(e.g., PDSCH), for a certain period of time on a certain componentcarrier(s) regardless of the MAC layer DRX parameters, (e.g., inactivitytimers, etc.), defined in the current LTE specification. The MAC layerDRX operation described in the current LTE specification may co-existwith the per-component carrier DRX operation in accordance with thisembodiment. In that case, the downlink channel, (e.g., PDSCH), may notbe received in a larger set of sub-frames than what would be receivedbased on the currently specified MAC layer DRX operation.

In accordance with the per-component carrier-DTX/DRX operation disclosedabove, cells may be permitted to be time-multiplexed within the samecomponent carrier and the best component carrier(s) may be selectedwithin a given time frame for the WTRU. FIG. 8 shows an exampleper-component carrier-DTX/DRX operation in accordance with oneembodiment. For example, in even-numbered frames, cell A may transmitcomponent carrier CC1A and cell B may transmit component carrier CC2B,and in odd-numbered frames, cell A may transmit component carrier CC2Aand cell B may transmit component carrier CC1B, as shown in FIG. 8. TheDRX/DTX periods for the WTRU may be set such that the DRX/DTX period fora given component carrier and cell corresponds to the time when thatcell is not transmitting that component carrier. It should be noted thatthe cells described may also be independent component carriers of acommon cell.

More generally, instead of turning on and off the component carriers,the transmit powers may be changed in different time frames. FIG. 9shows another example per-component carrier-DTX/DRX operation inaccordance with another embodiment. For example, the power used forcomponent carrier CC2A may be smaller than the power used for componentcarrier CC1A at cell A, and the power used for component carrier CC1Bmay be smaller than the power used for component carrier CC2B at cell Bin even-numbered frames, and the power used for component carrier CC1Amay be smaller than the power used for component carrier CC2A at cell A,and the power used for component carrier CC2B may be smaller than thepower used for component carrier CC1B at cell B in odd-numbered frames.The DRX/DTX periods at the WTRU may be set such that in even-numberedframes, the WTRU is in DRX/DTX in CC2A for cell A and DRX/DTX in CC1Bfor cell B and the opposite in odd-numbered frames.

The component carrier-specific reconfiguration (or handover) may beperformed in case coordinated multiple point transmission (CoMP) isimplemented. CoMP is a transmission and reception scheme that a WTRU mayreceive simultaneous transmissions from multiple cells or havetransmissions coordinated over multiple cells (such as coordinatedbeamforming or coordinated scheduling) and/or the WTRU transmissions maybe received at multiple cells in a coordinated way to improveperformance and avoid or reduce inter-cell interference. In accordancewith one CoMP scheme, scheduling may be dynamically coordinated acrossthe cells to control and reduce the interference between differenttransmissions. In accordance with another CoMP scheme, the transmissionsto the WTRU may be transmitted simultaneously from multiple transmissionpoints and the multi-point transmissions may be coordinated as a singletransmitter with antennas that are geographically separated.

In implementing the component carrier aggregation, control channels,(e.g., PDCCHs), for multiple component carriers may be separately codedinto separate messages and separately transmitted via each correspondingDL component carrier. This scheme is referred to as “separate codingseparate transmission.” Alternatively, the control channels, (e.g.,PDCCHs), may be separately coded into separate messages and all themessages may be jointly transmitted via one DL component carrier (DLanchor component carrier) from one cell. This scheme is referred to as“separate coding joint transmission.” Alternatively, the controlchannels, (e.g., PDCCHs), may be jointly coded into one message andtransmitted via one DL component carrier (anchor component carrier) fromone cell. This scheme is referred to as “joint coding jointtransmission.” DL shared channel(s), (e.g., PDSCH(s)), may betransmitted from multiple cells per component carrier and UL sharedchannel(s), (e.g., PUSCH(s)), may be received at multiple cells percomponent carrier.

In CoMP, when a joint transmission scheme is used (i.e., separate codingjoint transmission or joint coding joint transmission), a WTRU mayreceive a PDCCH from a single cell, (i.e., anchor cell), while receivingPDSCHs from, or transmitting PUSCHs to, multiple cooperating cells in anactive CoMP set. In accordance with one embodiment, in case where ajoint transmission scheme is used, (i.e., separate coding jointtransmission or joint coding joint transmission), a component carriercarrying the PDCCH may be handed over to a target cell, but a componentcarrier(s) for PDSCH and/or PUSCH may not be handed over to the targetcell. In the case of non-joint transmission CoMP, not all the PDSCHlinks may actually carry data for the WTRU, but rather coordinatedscheduling or coordinated beamforming may be used between the cells.

FIGS. 10A and 10B show an example component carrier-specificreconfiguration (or handover) when DL CoMP is implemented in accordancewith one embodiment. FIG. 10A shows before component carrierreconfiguration and FIG. 10B shows after component carrierreconfiguration. In FIG. 10A, WTRU 1002 receives downlink transmissionsfrom cell 1004 on component carriers 1A and 2A and from cell 1006 oncomponent carriers 1B and 2B. Cells 1004 and 1006 may be controlled bythe same eNB or different eNBs. Cell 1004 is currently an anchor cell (acell sending a PDCCH for the DL and/or UL transmissions), so that WTRU1002 receives a PDCCH from cell 1004 on component carrier 1A.

WTRU 1002 may not know that from which cell it is receiving the PDSCHtransmissions. As the trigger occurs with respect to component carrier1A in cell 1004, WTRU 1002 performs a handover of PDCCH from componentcarrier 1A to component carrier 1B in cell 1006, but not PDSCH, as shownin FIG. 10B. It should be noted that FIGS. 10A and 10B show handover inDL CoMP as an example, and the same may be applied to UL CoMP. In thecase of non-joint transmission CoMP, not all the PDSCH links shown inFIGS. 10A and 10B may actually carry data for the WTRU at a given time,but coordinated scheduling or coordinated beamforming may be usedbetween the cells, (e.g., cell 1004 transmits on CC1 and cell 1006transmits on CC2 at the given time). It should be noted that FIGS. 10Aand 10B show switching a channel from one cell to another, but it may beperformed within the same cell.

If a PDSCH(s) from multiple cells may not be received at the WTRU, thecomponent carrier-specific handover for the PDSCH may also be performed.Similarly, if a PUSCH(s) cannot be received at multiple cells, thecomponent carrier-specific handover for PUSCH may also be performed.Alternatively or additionally, an UL anchor component carrier carrying aPUCCH(s) may also be configured for the WTRU along with the DL anchorcomponent carrier carrying a PDCCH(s), and the componentcarrier-specific handover may be performed for either the DL anchorcomponent carrier, or the UL anchor component carrier, or both.

In accordance with another embodiment, when the WTRU is aware of theactive COMP set, (i.e., the cells from which the WTRU is receiving thePDSCH transmissions or to which the WTRU is transmitting the PUSCHtransmissions), the WTRU may perform the component carrier-specifichandover or reconfiguration for the PDSCH and/or PUSCH, independentlyfrom a PDCCH and/or a PUCCH. This is the case where the active CoMP setneeds to be changed for the WTRU, but the current anchor cell (for ULand/or DL) in the active CoMP set is not changed, so that the WTRU stillreceives a PDCCH from the same anchor cell or transmits a PUCCH to thesame anchor cell.

FIGS. 11A and 11B show an example component carrier-specificreconfiguration when DL CoMP is implemented in accordance with thisalternative embodiment. FIG. 11A shows before component carrierreconfiguration and FIG. 11B shows after component carrierreconfiguration. In FIG. 11A, WTRU 1102 receives downlink transmissionsfrom cell 1104 on component carriers 1A and 2A and from cell 1106 oncomponent carriers 1B and 2B. Cells 1104, 1106, 1108 may be controlledby the same eNB or different eNBs. Cell 1104 is currently an anchor cell(a cell sending a PDCCH for the DL and/or UL transmissions), so thatWTRU 1102 receives a PDCCH from cell 1104 on component carrier 1A. Asthe handover trigger occurs with respect to component carrier 1B in cell1106, WTRU 1102 performs a handover of PDSCH from component carrier 1Bto component carrier 1C in cell 1108, as shown in FIG. 11B while cell1104 remains the anchor cell. It should be noted that FIGS. 11A and 11Bshow handover in DL CoMP as an example, and the same may be applied toUL CoMP. It should be noted that FIGS. 11A and 11B show switching achannel from one cell to another, but it may be performed within thesame cell.

In order to support the component carrier-specific reconfiguration orhandover, (i.e., adding, removing or replacing at least one componentcarrier within the same cell or between cells), the WTRU may reportmeasurements to the network. The measurement may be any type ofmeasurement relevant to evaluating the channel quality including, butnot limited to, received signal code power (RSCP), reference signalreceived power (RSRP), signal-to-interference and noise ratio (SINR),reference signal received quality (RSRQ), or the like.

The WTRU may report component carrier-specific measurement of servingcell and/or neighboring cells, (e.g., measurement of every downlinkcomponent carrier or a subset of carriers, or the best measurement ofserving cell and/or neighboring cells); measurement of the anchorcomponent carrier of both serving cell and/or neighboring cells;weighted average measurement of all aggregated downlink carriers ofserving cell and/or neighboring cells, or the like.

The WTRU may report the measurements to the network to trigger componentcarrier reconfiguration or handover when the measurement of the servingcell is worse than the corresponding measurement of the neighboringcells by a preconfigured threshold. The threshold may be configurable.When the WTRU reports the measurement, the WTRU may sort the carriersand/or cells according to measurement values. The WTRU may be configuredto periodically report the measurement of any detected componentcarrier.

Scrambling codes may be designed such that signals from adjacent cellsmay have quasi-orthogonality. In this case, the component carrierreconfiguration or handover may be prioritized to the cell that exhibitsa better orthogonality of the scrambling codes, and the scrambling codeorthogonality metric may be considered as an additional measure forhandover.

In CoMP, the WTRU may report the measurements (or a subset of them) tothe network when the measurement (or some of measurements or a compositemeasurement) of the anchor cell is worse than the correspondingmeasurement(s) of the non-anchor cell(s) in the active CoMP set or theneighboring cells by a predefined threshold. This report may be used forPDCCH handover. The WTRU may report the measurements (or a subset ofthem) to the network when the measurements (or some of measurements or acomposite measurement) of the cells in the active CoMP set are worsethan the corresponding measurements of the neighboring cells by apredefined threshold. This reporting may be used for PDSCH handover. Theabove thresholds may be configurable.

Since with component carrier-specific reconfiguration or handover,(i.e., adding, removing or replacing at least one component carrierwithin the same cell or between cells), the WTRU may be connected tomore than one cells/eNBs at the same time, proper RRC signaling isneeded to support it. In accordance with one embodiment, RRC signalingto configure a split RRC connection between a source cell and a targetcell may be provided. A new (or modified) type of RRC connectionreconfiguration signaling may be defined including physical channelconfiguration. The RRC connection reconfiguration signaling may includefor the source cell and the target cell the following: PUCCHconfiguration, PUSCH configuration, sounding reference signal (SRS)configuration, uplink power control configuration, transmit powercontrol (TPC)-PDCCH configuration for PUCCH, TPC-PDCCH configuration forPUSCH, channel quality indication (CQI) or channel state information(CSI) reporting configuration, PDCCH search space configuration,assignment of the DL and/or UL anchor component carrier, assignment ofspecific preamble configurations, per-component carrier DTX/DRX patternconfiguration, (e.g., set of sub-frames where PUCCH and PUSCHtransmission is allowed), or the like.

The RRC configuration may be made with regard to a group of carriers inthe source cell and a group of carriers in the target cell.Alternatively, the RRC configuration may be made for each componentcarrier in the source and target cells.

The new or modified RRC message may include parameters for a number ofcomponent carriers, and the WTRU may try to perform component carrierreconfiguration, or handover to the component carriers, in the orderindicated in the RRC message. When the WTRU successfully performs acomponent carrier reconfiguration or handover to a particular componentcarrier the WTRU may send a component carrier reconfiguration orhandover complete message via that component carrier. On the networkside, the network may keep the resources on the component carriersindicated in the RRC message for the WTRU for a predefined period oftime, after which the resources may be released.

Alternatively, instead of providing the WTRU with a group of componentcarriers in a particular order, the network may provide the WTRU two (2)groups of component carriers: one group with a dedicated random accesschannel (RACH) preamble(s) and the other group with a contention basedRACH preamble(s). The WTRU may pick a component carrier on which theWTRU wants to initiate the handover. The WTRU may first select acomponent carrier from the group with a dedicated RACH preamble(s).

Optionally, the RRC message may indicate a component carrier(s) to whichthe WTRU may fall back in case of handover failure. The RRC message mayinclude a different set of RACH preambles for those carriers configuredfor fall back. In case of handover failure, the WTRU may look for thosecarriers as listed in the RRC message and try to re-establish aconnection on them.

To simplify the configuration and handover procedure, the configurationson the source component carrier subset may be transferred to the targetcomponent carrier subset, especially in the case of intra-cell componentcarrier-specific reconfiguration where the subset of UL and/or DLcomponent carriers are switched within the same cell. This may also beapplied to inter-cell handover.

If the WTRU has one or more component carrier that was already handedover to the target cell, the WTRU may not need to perform any extra stepto acquire the MIB and SIB information of the target cell since the WTRUalready obtained the MIB and SIB information of the target cell. If theWTRU does not have any component carrier that was handed over to thetarget cell, the WTRU needs to acquire the MIB and SIB information ofthe target cell.

In accordance with one embodiment, the source cell may signal all MIBparameters and important SIB parameters of the target cell to the WTRUin the handover command. Alternatively, the WTRU may acquire the MIB andall or some of SIBs of the target cell that are required to performuplink transmission (such as RACH, PUSCH/PUCCH) before handover.Alternatively, the WTRU may acquire the MIB and all or some of SIBs ofthe target cell that are required to perform uplink transmission (suchas RACH, PUSCH/PUCCH) after receiving the handover command but beforeperforming a random access in the target cell. Alternatively, the WTRUmay perform the handover procedure to the target cell, and aftersuccessful handover, the WTRU may acquire the MIB and SIB of the targetcell.

Embodiments for random access in component carrier-specificreconfiguration are disclosed hereafter. While a WTRU is performing arandom access on one or several of UL component carriers in the targetcell, the WTRU may continue its normal operation in the source cell. TheWTRU may perform a random access in the target cell as part of thecomponent carrier reconfiguration or handover procedure for the firstcomponent carrier that needs to be handed over to the target cell. Aftera successful component carrier reconfiguration or handover of the firstcomponent carrier to the target cell, the WTRU may not perform therandom access procedure in the target cell for the handover of theremaining component carriers to the target cell since the RRC connectionin the target cell has been established and uplink timing is aligned(i.e., synchronized).

In case a WTRU has a single radio capability, the WTRU may perform thecomponent carrier-specific reconfiguration or handover of a componentcarrier(s) by exploiting the inactivity period of the DRX cycle, (i.e.,opportunity of DRX period), on other component carrier(s) to initiate aRACH procedure with the target cell, while maintaining uplink anddownlink operation and connection with the source cell. As describedabove, the non-overlapping DRX and/or DTX patterns may be configured forthe component carriers.

FIG. 12 is a flow diagram of an example process 1200 of RACH procedurein accordance with one embodiment. For illustration, assuming that aWTRU is allocated with carriers 1D, 2D, and 3D in the downlink andcarriers 1U, 2U, and 3U in the uplink. The WTRU receives a handovercommand, (e.g., RRC_connection_Reconfiguration message with mobilityinformation) (step 1202). Assume that the handover command is receivedon component carrier 1D during its on-time duration. Since nonoverlapping DRX cycle may be configured for the component carriers,other component carriers (i.e., carriers 2D and 3D) may be inactive,(i.e., opportunity to DRX), during that time period. After receiving thehandover command, the WTRU synchronizes with the target cell whilecomponent carrier 2D, 3D and component carrier 2U and 3U are inactive(step 1204). The WTRU may initiate a RACH procedure to handover to thetarget cell with carriers 1U and 1D while component carriers 2D and 3Dand component carriers 2U and 3U are inactive (step 1206). The WTRU maycomplete the component carrier reconfiguration or handover procedurewith the target cell by using component carrier 1U and component carrier1D while carriers 2D, 3D and carriers 2U and 3U are inactive.Alternatively, certain steps of the RACH procedure may be provided witha higher priority than the on-duration time of the other carriers notinvolved in the RACH procedure.

In case of the component carrier-specific RACH procedure failure, theWTRU may inform the source eNB of the failure with an RRC message usingone of the still configured UL carriers (e.g., component carrier 2U or3U).

In case of success of the component carrier-specific RACH procedure, theWTRU may receive from the target cell an RRC_Connection_Reconfigurationrequesting the WTRU to reconfigure the other component carrier(s) thatare still configured with the source cell. As disclosed above, theprocedure to reconfigure the remaining component carriers may not beperformed through a RACH procedure since the WTRU is synchronized withthe target cell and obtained the necessary information.

Alternatively, the WTRU may maintain a subset of carriers (e.g.,component carrier 1D and 1U) with the target cell while maintaininganother subset of carriers (e.g., component carrier 2D, 3D, 2U, 3U) withthe source cell.

In case a WTRU has a dual radio capability, the WTRU may initiate a RACHprocedure on a subset of carriers (component carrier 1D, 1U in the aboveexample) with the target cell while maintaining the connection with thesource cell on the other carriers without the need of exploiting DRXinactivity. With the dual radio capability of the WTRU, the DRX patternson the component carriers may overlap.

An UL anchor component carrier carrying PUCCHs may also be definedsimilar to DL carriers carrying PDCCHs. In this case the RACH proceduremay be restricted to the assigned UL anchor component carrier.

The WTRU may handover to both an LTE-A cell and a WCDMA cell at the sametime. For example, a LTE 5 MHz component carrier and a WCDMA 5 MHzcomponent carrier, (or any other different system component carrier),may be aggregated.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs),Application Specific Standard Products (ASSPs); Field Programmable GateArrays (FPGAs) circuits, any other type of integrated circuit (IC),and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, Mobility ManagementEntity (MME) or Evolved Packet Core (EPC), or any host computer. TheWTRU may be used in conjunction with modules, implemented in hardwareand/or software including a Software Defined Radio (SDR), and othercomponents such as a camera, a video camera module, a videophone, aspeakerphone, a vibration device, a speaker, a microphone, a televisiontransceiver, a hands free headset, a keyboard, a Bluetooth® module, afrequency modulated (FM) radio unit, a Near Field Communication (NFC)Module, a liquid crystal display (LCD) display unit, an organiclight-emitting diode (OLED) display unit, a digital music player, amedia player, a video game player module, an Internet browser, and/orany Wireless Local Area Network (WLAN) or Ultra Wide Band (UWB) module.

What is claimed is:
 1. A long term evolution (LTE) base stationcomprising: a transmitter; and a processor, the processor configured tocoordinate with another LTE base station and, based on the coordination,determine subframes during which the LTE base station is to reducetransmission power so that the other base station can transmit on a samecarrier frequency in the determined subframes, the transmitter and theprocessor configured to send configuration information to a wirelesstransmit/receive unit (WTRU), the configuration information including amedium access control (MAC) based discontinuous reception (DRX)configuration and an indication of subframes during which the basestation is to reduce transmission power, and the transmitter and theprocessor further configured to transmit data to the WTRU in subframesbased on the determined subframes and the MAC based DRX configuration ofthe WTRU.
 2. The LTE base station of claim 1, the processor and thetransmitter further configured to transmit an indication to the WTRU ofa first set of subframes associated with first power control parametersand a second set of subframes associated with second power controlparameters.
 3. The LTE base station of claim 2, wherein the first andthe second sets of subframes are based on the determined subframes. 4.The LTE base station of claim 1, wherein, in the determined subframes,the processor and the transmitter are further configured to not transmitphysical downlink shared channels (PDSCHs).
 5. The LTE base station ofclaim 1, the processor and the transmitter further configured totransmit a signal including radio resource control informationconfiguring component carriers for both the base station and the otherbase station.
 6. A long term evolution (LTE) wireless transmit/receiveunit (WTRU) comprising: a receiver; and a processor, the receiver andthe processor configured to receive configuration information from abase station, wherein the configuration information includes a mediumaccess control (MAC) based discontinuous reception (DRX) configurationand an indication of subframes during which the base station is toreduce transmission power, wherein the reduced transmission powersubframes allow another base station to transmit on a same carrierfrequency as the base station in determined subframes, and the receiverand the processor further configured to receive data from the basestation in subframes based on the determined subframes and the MAC basedDRX configuration of the WTRU.
 7. The LTE WTRU of claim 6, the processorand the receiver further configured to receive an indication from thebase station of a first set of subframes associated with first powercontrol parameters and a second set of subframes associated with secondpower control parameters.
 8. The LTE WTRU of claim 7, wherein the firstand second sets of subframes are based on the determined subframes. 9.The LTE WTRU of claim 6, the processor and the receiver furtherconfigured to receive a signal including radio resource controlinformation configuring component carriers for both the base station andthe other base station.
 10. A method, implemented by a long termevolution (LTE) base station, the method comprising: coordinating, bythe LTE base station, with another LTE base station and, based on thecoordination, determining subframes during which the LTE base station isto reduce transmission power so that the other base station can transmiton a same carrier frequency in the determined subframes; sending, by theLTE base station, configuration information to a wirelesstransmit/receive unit (WTRU), wherein the configuration informationincludes a medium access control (MAC) based discontinuous reception(DRX) configuration and an indication of subframes during which the basestation is to reduce transmission power; and transmitting, by the LTEbase station, data to the WTRU in subframes based on the determinedsubframes and the MAC based DRX configuration of the WTRU.
 11. Themethod of claim 10, further comprising transmitting, by the LTE basestation, an indication to the WTRU of a first set of subframesassociated with first power control parameters and a second set ofsubframes associated with second power control parameters.
 12. Themethod of claim 11, wherein the first and the second sets of subframesare based on the determined subframes.
 13. The method of claim 10,wherein physical downlink shared channels (PDSCHs) are not transmittedin the determined subframes.
 14. The method of claim 10, furthercomprising transmitting, by the LTE base station, a signal includingradio resource control information configuring component carriers forboth the base station and the other base station.